The present invention relates generally to stator vanes in compressors of a gas turbine engine and, in particular, to the damping of vibrations transmitted to such stator vanes from the case of the engine.
It has been found that the case of a gas turbine engine vibrates at various modal frequencies during engine operation. These modal vibrations typically have a wide range of mode shapes, as well as different levels of displacements. It will be appreciated that the fixed stator vanes for the low pressure compressor and/or the high pressure compressor of the engine are generally attached to the engine case. This may be accomplished, for example, by sliding the stator vanes into rails supplied on the inner surface of the case or by capturing a flange between a split-line in the case. In both instances, at least some of the vibration energy of the engine case is transmitted to the stator vanes. Since the individual stator vanes and/or the shroud systems for such stator vanes can vibrate at frequency modes which are substantially synchronous with the case modes, the potential for wear damage and/or high cycle fatigue damage is created.
In order to prevent such potential damage, gas turbine engines in the prior art have employed a variety of solutions. One solution has been to redesign the engine case to remove the potentially damaging modes of vibration. Another solution has been to redesign the stator vanes or the vane/shroud system to remove the vibration modes which are synchronous with the case vibration modes. Damping material and other vibration damping devices have also been added in the shroud/vane tip area to damp the vibrations experienced by such stator vanes, as evidenced in U.S. Pat. No. 4,872,812 to Hendley et al. and U.S. Pat. No. 6,343,912 to Manteiga et al. Still another solution has been to add a mechanical damper spring to the base of the stator vane, as seen in U.S. Pat. No. 5,681,142 to Lewis. None of these solutions, however, has been seen to positively effect a change in the vibrations experienced by the stator vanes from the engine casing.
Accordingly, it would be desirable for a stator vane assembly to be developed which damps the vibrations from the engine case to the stator vanes of the compressor. It is also desirable for the stator vane assembly to be easily assembled and disassembled to facilitate manufacturing and repair.